Periodic wave repeater



. Aug. 20, 1940.. .DQ E. HARNETT PERIODIC WAVE REPEATER Filed Dec. 15, 1938 FIG.6.

INVENTOR D IEL E. HARNETT ATTORNEY i Patented Aug. 20, 1940 UNITED STATES iwrE'N'rl OFFICE anzuzernmonro ways marsa Daniel E. namen, nance, 1v. Y.. mor u Ilaaeltine` Corporation, a corporation of Dela- This invention relates to periodic wave repeaters and more particularly to such repeaters which are substantially insensitive to undesired control pulses or .tol extraneous transients during I the greater portion of each period intervening between successive output pulses;

In many applications of periodic wave repeeters, it is essential that the. repeater be extremely stable ln operation and that the occurl rence of the periodic pulses be precisely timed in phase and frequency with respect to a reference or controlling standard. It has heretofore been proposed to improve the stability of such repeaters by reducing to a minimum the portion l of the cycle during which the repeater' is sensitive to a control influence, thus reducing the chances that it will be triggered by extraneous transients or undesired control pulses to produce a spurious output pulse. One embodiment oi.' this zo feature is disclosed and claimed in a copending application of Harold A. Wheeler and John C. Wilson, Serial No. 236,200, illed October 21, 1938,

' f in which the repeater is normally maintained insensitive and is sensitizedby means of a delay- -iilter network or transmission line which feeds back delayedpulses from the output circuit of the repeater to the.sensitivity-controlling circuit to determine the successive output pulses. Such an arrangement h as the advantage of an extreme accuracy in determining the interval separating successive pulses which cannot be obtained by many timing circuits, for example, those includl ring resistance 'the impedance value of whichehanges with temperature and other operating as conditions. v

The present invention constitutes an improvement on the periodic wave repeater of the type described and claimed in the above-mentioned pplication of Wheeler and Wilsonin which the 40 iming-delay network is not included. in a feedback path from the output circuit to the sensitivity-controlling circuit of the repeater but is individual to the sensitivity-controlling circuit.v

u rt a a finther object 4i.' the invention to' provide an improved periodic wave repeater in which the period thereof is dependent solely on an electrical-delay network as distinguished from a concentrated resonant circuit or a disslpative time yconstant circuit.

. 5 lftA is afurther object of the invention to provide an improved periodic wave repeater the operation and -period of which are dependent solely upon predetermined pulses vwhich may be selected from a series of pulses and disturbances such 10 as static.

It isv an object of the invention, therefore, to provide an improved pulse wave repeater for producing output pulses which.k are precisely timed by one edge of only selected pulses of' an la `input-timing pulse signal.

vIt is a more speciilc object of the invention to provide a pulse wave repeater in which a. delayed derived pulse and an undelayed input pulse cooperate in'such manner that the initiation of an 20 output pulse is responsive solely to the leading edge of such undelayed input signal. 1t is a further object of the invention to provide an improved submultiple generator or frequ'e'ney divider which is insensitive except during 25 predetermined intervals determined by a delay i network, the timing of which depends mainly on 'stable capacitance and inductance values as dis- Y there is veffectively a time delay approximately equal tothe desired period of the output pulses of the repeater. Means are also provided so coupling the terminals of the delay network to the 40 sensitivity-controlling circuit that the delay network derives an input pulse from said sensitivitycontrolling circuit at the time an output pulse of saidrepeater is being generated and applies a delayed pulse to said sensitivity-controlling circuit with such a delay and with such polarity as to sensitize said repeater at the time the succeeding output pulse from said repeater is due.

In a preferred embodiment of theinvention, the repeater comprises a vacuum tube adapted to u produce relaxation oscillations.

In accordance with a further feature of the in.- vention, a pulse-wave repeater stage for producing output pulses comprises a. repeater device having input and output circuits, one of which is u 2 l adapted to have applied thereto a signal including a pair of pulses with predetermined time separation. Means are included in the repeater device and its associated circuits for maintaining the stage normally insensitive to the above-mentioned pulses alone. Means are further provided for deriving from the rst pulse of the pair a pulse` delayed for a time less than the abovementioned predetermined time and having a duration such that it coincides in time with the second pulse of the pair for a predetermined interval, together with means including the repeater device responsive jointly to the delayed pulse and to the above-mentioned second pulse for deriving an output pulse only ,during the above-mentioned predetermined interval. l

As used in this specification, the term delay network is defined as one in which the time delay of a narrow pulse transmitted through the network is at least twice as great as the broadening of the pulse by the network, the time delay being measured as the time interval between the transmitted pulse in the input circuit and the peak of the pulse in the output circuit of the network, and the broadening eiect being measured as the increase in the time duration of the output pulse at half the peak amplitude caused by its transmission through the network. In a wave iiltermade up of lumped reactance elements, several'sections are necessary to provide a delay network..

In accordance with'a preferred embodiment of the invention, synchronizing pulsesy are also applied to the input circuit of the wave generator and the time at which the generator is triggered to produce-an output pulse is dependent upon the joint occurrence of the synchronizing pulse and the delayed pulse from the delay network. In the absence of either of these two pulses, therefore, the generator is maintained in- -For a better understanding'of the invention,

togetherv with other and further objects thereof, reference is had tothe following description taken' in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Figs. 1, 3, 5, and 6 are circuit diagrams, partially schematic, of different embodiments of the invention; Figs. 2a--2d illus- 'charged between successive discharges from a direct current supply circuit comprising a suitable source, such as a battery I2, and a resistor I3. Vacuum tube I0 has a control grid which is normally biased partially or completely'to cutoi by an input circuit including a bias source, such as a battery I 4 and a resistor I5. In order that thecircuit of Fig. 1, comprising a high vacuum tube I0, may operate as a conventional relaxaaaiacao y tion oscillator, there is provideda feed-back coupling comprising an inductor I8 in the input circuit of tube I0 inductively coupled to an inductor I'I in the output circuit thereof, though it will be understood that this feed-back circuit may be omitted in case a vapor or gaseous electron-discharge tube is utilized. synchronizing signals may be applied to the input circuit of vacuum tube I Il from asuitable source lI8 through coupling condenser 22. A delay network 24 is included in the output circuit, which is the sensitivity-controlling circuit of the system of Fig. 1. This delay network may be aluniform transmission line, a uniform artificial line, ora wave lter composed of lumped reactance elements, and is shown as a simple uniform transmission line havimage impedance at junction terminals 20 to y provide a two-terminal voltage-reversing reecting lter. As shown in the drawing, junction terminals 2G are short-circuited. Terminals I9 are connected in series with condenser I I in the output, or sensitivity-controlling circuit, of vacuum tube I0.

Reference is made to Figs. 2a- 2d for an'exl planation of the operation of the circuit of Fig. 1. Fig. 2a represents a synchronizing signal having one or several pulses per output cycle, three being shown as an example. In case the synchronizing signal of Fig.- 2a.y is utilized, the device operates as a frequency divider by synchronizing at a submultiple frequency. Fig. 2bV shows the starting pulsel of current in the outputl circuit of tube I0` which may be initiated byv momentarily decreasing theA negative grid bias of battery I 4 during the voccurrence of a synchronizing pulse. This pulse is built up by the feedback through inductors I6, Il of the relaxation oscillator and is quickly chopped oil by the discharging of the condenser II. The pulse of current of Fig. 2b flowing through condenser II and resistor 2l causes a voltage pulse of negative polarity to travel down the transmission line 24 toward junctionterminals 20 and to be reflected after a predetermined time delay with opposite polarity.

Fig. 2c shows the later arrival of the reflected becomes conductive with a synchronizing pulse applied to its grid-cathode circuiti The characteristic of Fig. 2d, during thetime interval tz-ts when the reected positive pulse.

from terminals I9 is-injected into the output or sensitivity-controlling circuit, indicates that the tube will be red during this interval if a synchronizing pulse simultaneously occurs during the interval. The time delay of delay network Mis made to be only slightly smaller than theA period of the synchronizing pulsesby which it is desired to control the oscillations. Under these conditions, it will be understood that each ring of the tubel is determined precisely by the instant at which a pulse of Fig. 2a is applied to its input circuit and a positive pulse ofl Fig. 2c occurs in its output circuit. Immediately after firing, a negative pulse is developed across ter- 75 minals I9, this negative pulse travelling forward and backward through delay 'network .24 and appearing as a positive pulse at terminals I9 to initiate the next ilring of tube III. delay of line, 24 is very slightly less than the period of the synchroniaing pulses, it will be seen that vacuum tube I0 is maintained nonconductive over the greater portion of the operating cycle and is conditioned'ior operation by a pulse applied from the delay network 24 in each instance just in time for the occurrence of the desired synchronizing pulse in the'input circuit of the tube I0, thereby rendering'the periodic wave generator insensitive to undesired controlling iniiuences until the time it is desired to effect operation by a selected synchronizing pulse. l

It will be understood that the source of synchronizing signals I8 may be omitted, in which case the perodicity of the wave generator of Fig. 1 is controlled solely by the time delay of line 2,4. Furthermore, the circuit may be Yso adjusted that, even in the absence of a reflected pulse, corresponding to that of Fig. 2c, the output voltage `wou1d eventually rise above the level o! the dotted line of Fig. 2d. Under .these conditions the circuit is self-starting after a failure to ilre due, for instance, to interference just at the time the circuit would ordinarily ilre.

The periodic wave generator of Fig. 3 is essentially similar to that of Fig. 1 and similar circuit elements have been given identical reference numerals. The circuit of Fig. 3 differs from that of Fig. l -primarily in that condenser H, which is the principal anode voltage-determining element in the circuit of Fig. 1, has been omitted in the circuit of Fig.` 3. Thus, the potentialacross terminals I9 of delay network 24 in the circuit of Fig. 3 becomes substantially the sole factor in determining the variations of the anode voltage of tube Ill about its mean value which is the voltage of battery I2. Output terminals 29, 25 coupled across a resistor 25 in the anode circuit of tube I0 are also provided in the circuit of Fig. 3. It will be understood that the output means including coupling. resistor 25 and output terminals 29, 26 is of a type well known in the art and that no novelty is claimed therefor either alone or in combination with other elements of the repeater circuit.

In considering the operation of the wave repeater of Fig. 3, reference is made to Fig. 4 in which curve A represents a periodic-pulse input wave supplied by source I9; curve B, the pulse current wave developed in the output circuit of tube I0, which is similar to the pulse voltage wave developed across the input terminalsl I9, I9 of delay network 24; curve C, the delayed reflected voltage p ulse wave appearing across the inputterminals I9, I9 of the delay network; and curveD the anode-voltage timey characteristic of the repeater tube III. Assuming that, at instant ti, the anode voltage of tube I0 is at a value ei such that the tube is fired by an input pulse a1 from source I8 applied to its input circuit, a negative voltage pulse b1 is generated across the input terminals I9, I9 due to the output current of similar wave form flowing through resistor 2| in the time interval t 1tz accompanied by a rapid fall of anode potential di. Such negative voltage pulse b1 is translated bythe network 24 and reected from its remote junction terminals 2n, 20 with opposite polarity as a delayed positive-voltage pulse c appearing across terminals I9, I9 after .a delay t1--t'a, which yis slightly less than the predetermined time ti-n o! sepa- Since the vcoincides in time with the second pulse az for a predetermined interval t4-ts during which time the tube I0 is again firedl by the second input pulse an. applied to its grid to repeat the cycle.

Output voltage pulses corresponding to the output'current pulses baba are developed across the coupling resistor 25 and appear at the output terminals 26, 26. There is no reflection of the delayed voltage pulse c at the terminals I9, I9 of the delay network 24 because the impedance of the resistor 2I substantially matches its image impedance.

During the time t2-ts, the anode potentlalD of the output circuit does not rise above the steady state value e2 of battery I2 which is so `related to the grid bias derived from battery I4 that the tube I0 is entirely insensitive to all input pulses including'nonselected pulses an, a4 of the input pulse wave of curve A intervening between the selected pair of pulses a1, a2. However, at the instant t'a the delayed positive pulse c is applied to the output circuit so that the anode potential rises rapidly at dz and the tube is in a condition to be fired at instant t4 by the leading edge of the selected second input pulse aa to produce the desired output pulse initiating precisely at the time t4 and persisting during the interval t4-t5 in which the tube I0 is conductive. The anode potential during this interval t4-ts falls rapidly at d3 below the normal anode potential ez due to the feed-back coupling I6, I1 between the input and output circuits. The Aanode potential then returns to its normal value due to the discharge current developed by .the collapse of the magnetic ileld of windings I6, I1 which ows into the inherent capacitance of the output circuit either gradually or rapidly, as indicated at d4, depending upon the circuit constants.

It will be noted that the reilected voltage pulse c is not only somewhat widened but that it is also somewhat degraded due to the fact that the transmission characteristics oi' delay network 24 are not ideal. Therefore, the leading edge of the reflected voltage pulse is not as steep nor as precisely timed as the corresponding edge of the input pulse. In accordance with the invention, by making the delay of illter network 24 slightly less than the time separation of successive input pulses, the tube III is conditioned -to re only upon the leading edge of the original input pulse and is thus nearly independent of the transmission properties o f the delay network.

From av consideration of the circuit of Fig. l, it will be seen that resistor I3 and condenser II are utilizedas a circuit to provide, an approximate time constant lfor the operation of the system. It will also be understoodthat resistor I5 and grid condenser 22 also have an eiect upon the operation of the system of Fig. 1 but that the operation of Fig. l may be as above described if resistor I3 and condenser II are so proportioned as to -be controlling factors in the circuit. The circuit of Fig. 5 is generally similar .to that of Fig. 1 and' similar circuit elements have been given identical reference numerals. mary difference in the circuitof Fig. 5 and that of Fig. 1 is that the elements I3 and II have/ been omitted and resistor I5 and condenser 22 are made to be the time-cQnstant-determining elements. Also in the circuitaof Fig. 5, the delay The pri'- network 2S is included in the input circuit of vacuum tube Ii, which is in this case the sensitivity-controllingcircuit.

The operation of the circuit of Fig. 5 is generally similar to that of Fig. 1 and it is believed that no further description thereof is necessary for a complete understanding of the arrangement.

'I'he circuit of Fig. 6 is generally similar to that' of Fig. 3 and similar circuit elements have been given identical reference numerals. 'Ihe primary difference in the circuits is that in Fig. 6 the delay network 24 is included only in the input circuit of vacuum tube I0, which is the sensitivity-controlling circuit, instead of in the output circuit as in Fig. 3. 'The operation of the system of Fig. 6 is generally similar to that oi' Fig. 3 and no further explanation is believed to be necessary.

The primary difference between. the embodiments of the invention illustrated in Figs. 1 and 5 and those oi.' Figs. 3 and 6 is in the relation between cutoi amplitudes of the tube and the amplitude of the triggering pulses. l Thus, in the case of Fig. l, the arrangement may be biased considerably below the cutofi point. During the charging period the anode voltage rises so that a relatively small delayed voltage from the delay network is sumcient to bias the tube to'an operative condition. In the circuit of Fig-3, on the other hand, there is no voltage rise corresponding to that of condenser il of Fig. 1 and the pulse fed back by the delay network must alone be sufficient to cause the tube i0 to become conductive.

While there have been describedwhat are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the truey spirit and scope of the invention. 7

What is claimed is:

1. A periodic wave repeater for producing I periodic output pulses comprising, a repeater device having an input circuit and an output circuit, one of said circiits constituting' a sensitivity-controlling circuit, a delay network having a plurality of terminals between which there is effectively a time delay approximately equal to the period of the output pulses of said repeater, and means so coupling said terminalsof said network to said sensitivity-controlling circuit that said network derives an input pulse from said sensitivity-controlling circuit at the time an output pulse of said repeater is being generated and applies a delayed pulse to said sensitivitycontrolling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse from said repeater is due.

2. A periodic wave repeater for producing periodic output pulses in response to periodic input pulses comprising, a vacuum tube including an input circuit and an output circuit, one of said circuits constituting a sensitivity-controlling circuit, a delay network having a plurality of terminals between which there is effectively` a time delay approximately equal to the period of the output pulses of said repeater, and means so coupling said terminals of said network only to there is effectively a time delay approximately said sensitivity-controlling circuit that said network derives from certain of said periodic input pulses a delayed pulse occurring during a predetermined succeeding input pulse and applies said delayed pulse' to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse o! said repeater is due.

3. A periodic wave generator for producing periodic output pulses in response to input pulses comprising, a vacuum tube having an input circuit and an output circuit. said vacuum tube and circuits comprising means for producing relaxation oscillations, a time constant circuit having a plurality of terminals between which there is I polarity asto sensitize said vacuum tube at the time the succeeding output pulse from said generator is due.

4. A periodic wave generator for producing periodic output pulses in response to input pulses comprising, a vacuum tube having an input circuit and an output circuit, said tube being biased considerably beyond cutoff, said vacuum tube and circuits comprising means for producing ref laxation oscillations, a time constant circuit having a plurality ofterminals between which there is eiectively a time delay approximately equal to the period oi the output pulses of said generator, and means so coupling said terminals only to one of said input and output circuits that said time constant circuit derives an input pulse from one of said circuits at the time an output pulse of said generator is being generated and applies a 'delayed pulse to said one of said circuits with such polarity as to condition said tube near its cutoi point at the time the succeeding output.. pulse from said generator is due.

5. A periodic waveA generator for producing periodic output pulses in response to input pulses comprising, a vacuum tube having an input circuit and an output circuit. said vacuum tube and circuits comprising'means for producing relaxation oscillations, one of said circuits constituting a sensitivity-controlling circuit, adelay network having a plurality of terminals between which there is effectively a time delay approximately equal to the period of the output pulses of said generator, and means vso couplingsaid terminals of said network only to said sensitivity-controlling circuit that said network derives an input pulse from said sensitivity-controlling circuit at the time an output pulse of said generator is being generated and applies a delayed pulse to said sensitivity-controlling circuit withl such polarity as to sensitizesaid tube at the time the succeeding output pulse from said generator ,is

due to determine the periodicity of said oscillations. 'v

6. A periodic wave generator for producing periodic output pulses in response to periodic,

input pulses comprising, a vacuum tube having an input circuit and output circuit, means including a feed-back coupling between said circuits for causing said tube to produce relaxation oscillations, one of said circuits constituting al sensitivity-controlling circuit, a delay network having a plurality of terminals between which equal to the period of the output pulses of said generator, and means' so coupling said terminals ci' said network only to said sensitivity controlling circuit that said network derives an inputl pulse from said sensitivity-controlling circuit at the time an output pulse of said generator is being generated and applies a delayed pulse to prising, ya repeater device having an irput circuit and an output circuit, one of said circuits constituting a sensitivity-controlling circuit, a delay network having a plurality of-terminals between which there is eiectively a time delay approximately equal to a predetermined multiple of the period of said input pulses of saidrepeater, and means so coupling said terminals of said network only to said sensitivity-controlling circuit that said network derives an input pulse from said sensitivity-controlling circuit at the time' an output pulse of said repeater is being generated and applies a delayed pulse to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse from said repeater is due.

8. A periodic wave repeater for producing periodic output pulses comprising, a repeater device having an input circuit and an output circuit, one of said circuits constituting a sensi- I tivity-controlling circuit, and a delay network included only in said sensitivity-controlling circuit and having a time delay approximately equal to the period of 'the output pulses of said repeater, said delay network comprising terminals coupled in said sensitivity-controlling circuit and including a reiiecting filter having a voltage-reversing reecting junction remote from said terminals and being terminated at said terminals to prevent reflection thereat, said network being connected to derive an input pulse from said sensitivity-controlling circuit at the time an output pulse of said repeater is being ,generated and to apply a delayed pulse to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse f said repeater is due.

9. A periodic wave repeater for producing periodic output pulses comprising, a repeater device having an input circuit and an output circuit, said outputcircuit constituting a sensitivity-controlling circuit, a delay network having a plurality of terminals between which there is effectively a time delay approximately equal to the period of the output pulses of the said repeater, and means so coupling said terminals of said network only to said sensitivity-controlling circuit that said network derives an input pulse from vsaid sensitivity-controlling circuit at the time an output pulse of said repeater is'being generated and applies a delayed pulse to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse of said repeater is due.

10. A periodicl wave repeater for producing periodic output pulses comprising, a .repeater device having an input circuit and an output circuit, said input circuit constituting a sensitivitycontrolling circuit, a delay network having a plu- A-ns means so coupling said terminals of said network only to said sensitivity-controlling circuit that said network derives an input pulse from said sensitivity-controllingcircuit at the time an output pulse of said repeater is being generated and applies a delayed pulse to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output pulse fromsaid repeater is due.

11. A periodic wave repeater for producing periodic output pulses comprising an inputcircuit and an output circuit, one of said circuits l constituting a sensitivity-controlling circuit, and a delay network included only in said sensitivity.- controlling circuit and having a time delay approximately equal to the period of the output pulses of said repeater, said delay network comprising, a two-terminal voltage-reversing reflecting iilter, an impedance coupled across the terminals of said iilter and substantially matching the image impedance thereof to prevent reflection thereat, the terminalsof said lter being coupled in said sensitivity-controlling circuit and the impedance across said terminals comprising the major impedance of said sensitivity-controlput pulse from said sensitivity-controlling circuit at the time an output pulse of said repeater is being generated and applies a delayed pulse to said sensitivity-controlling circuit with such polarity as to sensitize said repeater at the time the succeeding output p-ulse from said repeater is due.

12. A pulse wave repeater stage for producing output pulses comprising, a repeater device having input and output circuits one of which is adapted to have applied thereto a signal including a pair of pulses with predetermined time separation, means comprised in said repeater device and its associated circuits for maintaining the stage normally insensitive to said pulses alone, means for deriving from the first pulse of said pair a pulse delayed for a time less than said predetermined time and having a duration such that it coincides in time with the second pulse of said pair for a predetermined interval, and means including said repeater device responsive jointly to said delayed pulse and said second pulse for deriving an output pulse only during said predetermined interval.

13. A periodic-pulse wave repeater stage for producing periodic output pulses comprising, a

repeater device having input and output circuits v one of which is adapted to have applied thereto a periodic-pulse wave with predetermined time separation between pulses, means comprised in 14. A pulse wave repeater stage for producing I output pulses comprising, a repeater device having input and output circuits one of which is adapted to have applied thereto a signal including a pair of pulses with predetermined time separation, means comprised in said repeater device and its associated circuits for maintaining ithe stage normally insensitive to said pulses alone, a

25 ling circuit, whereby said network derives an in- 55 said repeater device and its associated circuits s reecting polarity-reversing .delay filter coupl than said predetermined time and having a duration such that it coincides in time with the second pulse of said pair for a predetermined interval, and means including said repeater device responsive jointly to said delayed pulse and said second pulse for deriving any output pulse only during said predetermined interval.

15. A pulse wave repeater stage for producing output pulses comprising, an input circuit adapted to have applied thereto a pair of pulses with predetermined time separation and including means for deriving from the nrst pulse of said pair a pulse delayed for a time less than said predetermined time and having a duration such that it coincides in time with the second pulse of said pair for a predetermined interval and means for combining said second and delayed pulses to develop a pulse greater in amplitude than either, pulse-responsive means coupled to said input circuit and responsive to said combined pulses, and

` means included in said input circuit for maintaining said last-named-means normally insensitive to any of said pulses alone.

16. A pulse wave repeater stage for producing output pulses comprising, a repeater device having input and output circuits one of which is adapted to have applied thereto a signal including a pair of pulses with predetermined time separation, means comprised in said repeater device and its associated circuits for maintaining the stage normally insensitive to said pulses alone, means coupled to said one of said circuits for deriving from the iirst` pulse of said pair a pulse delayed for a time less than said predetermined time and having a duration such that it coincides in time withthe second pulse of said pair for a asias predetermined interval, and means including said repeater device responsive jointly to said delayed put pulse only during said predetermined interval. 17. A pulse wave repeater stage for producing output pulses comprising, a repeater .device having an output circuit and an input circuit adapted pulse and said second pulse for deriving an outfirst pulse of'said pair a pulse delayed for a time` less than said predetermined time and having a duration such that it coincides in time with the second pulse of said pair for a predetermined interval, and means including said repeater device responsive jointly to said delayed pulse and said second pulse for deriving an output pulse only during said predetermined interval.

18. A pulse wave repeater stage for producing output pulses comprising, a repeater. device having an output circuit and an input circuit adapted to have applied thereto a signal including a pair of pulses with predetermined time separation, means comprised in said repeater device and its associated circuits for maintaining the l'stage normally insensitive to said pulses alone, means coupled to said input circuit for deriving from the iirst pulse of said pair a pulse delayed for a time less than said predetermined time and having va duration such that it coincides in time with the second pulse of said pair for a predetermined interval, and means including said repeater device responsive jointly to said delayed pulse and said second pulse for deriving' an output pulse only during said predetermined interval.

DANIEL E. HARNEI'I. 

